According to the letter, the PTA says blocking the texts is meant to control spamming, which it defines as "the transmission of harmful, fraudulent, misleading, illegal or unsolicited messages in bulk to any person without express permission of the recipient."

Mobile phone companies Telenor Pakistan and Ufone confirmed to BBC News that they had received the memo and the "dictionary."

A spokesman for the PTA, meanwhile, told The Guardian newspaper that the move was in response to complaints from customers who said they were receiving offensive text messages.

"Nobody would like this happening to their young boy or girl," Mohammad Younis said.

Pakistanis have been reacting to the news on Twitter, sometimes wondering what the words and expressions mean.